FIG. 8 shows a conventional chain transmission 500, in which a transmission chain 510 is engaged with a sprocket 520, having a tooth form as defined in ISO 606:1994(E). This chain transmission is described in U.S. Pat. No. 5,427,582. As shown in FIG. 9, in the conventional chain transmission 500, as the chain rollers R engage a sprocket, they contact the bottoms 522a of the gaps between sprocket teeth 522. As a result, polygonal movement of the chain is generated.
Polygonal movement of the chain causes vertical motion of the chain as it approaches and moves away from the sprocket (that is, motion of the chain in a direction transverse to its direction of travel but in the plane defined by its loop-shaped path of travel). The vertical motion induces chordal vibration in the chain, which, in turn, generates vibration noise. The vertical motion of the chain also causes impact sounds as the rollers R of the approaching portion of the chain come into engagement with the tooth gap bottom 522a on the sprocket. These impact sounds are responsible for significant amounts of noise generated in the operation of the conventional chain transmission. The polygonal motion of the chain also causes changes in speed along the direction of travel of the transmission chain, which also impairs smooth transmission of power.
Objects of this invention are to provide a chain transmission in which vertical motion of the chain, due to polygonal movement during engagement of the chain with the sprocket, is suppressed, in which changes in the speed of the chain are suppressed, and in which vibration noise and impact sounds are also suppressed so that low noise operation can be realized.